This invention relates to certain azomethine compositions and to monoazo pigments modified by such azomethine compositions.
Monazo pigments represent an important class of colorants for coatings and printing inks. Various methods have appeared in the prior art for improving the properties of such pigments. For example, U.S. Pat. No. 4,720,304 describes the use of imidazole-modified dyes to impart enhanced tinctorial strength, rheology and printing properties to such pigments. Preparation of the modifying compounds requires the use of formaldehyde and the resultant dyes are very system specific due to their substantial tinctorial power. In contradistinction thereto, the azomethine compositions of the present invention contribute relatively little coloration effects due to their high molecular weights. In a similar vein, U.S. Pat. No. 4,664,714 discloses the use of cyanuric chloride-modified dyes to impart improved gloss rheology and stability, but this method has limitations similar to those of U.S. Pat. No. 4,720,304.
U.S. Pat. No. 4,341,701 teaches that pigments exhibiting improved flow properties, increased color strength, increased transparency and improved dispersability can be prepared by a two-step coupling method. However, that technique is less economical and more prone to the generation of impurities which can result in "dirty" shades. Other patents such as U.S. Pat. Nos. 4,415,705; 4,812,517; 4,762,568 and British Patent 1,510,190 teach of the use of colorless polymeric pigment dispersants, but none of the methods disclosed in such patents have been found to be as effective as the compositions and methods of the present invention.